Adjustable mechanical arms of the type to which this specification pertains are commonly found in offices, laboratories, studios and other locations to support objects such as lamps, computer screens, laboratory instruments, microphones, etc. at a variety of different angles and heights.
Typical prior art lamps of the type commonly available generally consist of an upper and a lower arm pivotally joined at a mid-point. The lower arm may also be pivotally connected to a stationary base. Such arms are typically constructed using a plurality of parallel mechanical linkages for each arm segment that are pivotally joined at various points by parallelogram shaped structures. The typical prior art mechanical arm structure is counterbalanced using a spring which is connected diagonally between one of the parallel linkages and the parallelogram structure at the joint, such that any movement of the arm around the joint will cause an expansion or contraction of the spring to counterbalance the weight of the object being supported at the length of the arm. Arms of this type are illustrated, for example, in U.S. Pat. No. 4,953,822 (Sharber, et al.) and U.S. Pat. No. 6,550,734 (Spadea).
The prior art arms, however, exhibit several unsatisfactory characteristics. First, the arms are somewhat unsightly, having all the mechanical components in plain view, including the linkages, the parallelograms, the springs, the electrical cord and all hardware used to hold the various parts of the arm together. Additionally, the design is often difficult to keep clean as dirt and dust tends to collect in the nooks and crannies of the device, and is expensive to manufacture, both in terms of number of parts and time to assemble.
Therefore, it would be an object of the current invention to provide a design which is more aesthetically appealing than the current prior art designs wherein the mechanical components are hidden inside an enclosure and further wherein the electrical cable is not visible. It would be a further object of the invention that the lamp have no sharp edges or nooks and crannies into which dirt and dust can collect and have fewer part than prior art designs such that manufacturing costs are reduced.
Another problem with designs of the prior art is that the spring counterbalance may not exert a constant force on the object being supported at all positions of the upper and lower arm portions. For example, at the far edges of the range of motion, it is usually the case that insufficient force or an excess of force be exerted on the object being supported, making it difficult and cumbersome to place the object in positions at the extremes of the ranges of motion of either portions of the arm. Additionally, a user of the arm should not be required to use excessive force to move the object being supported to the desired position.
It would therefore also be an object to make the spring pressure more consistent over the entire range of motion of both arms of the device and to minimize the amount of force that must be applied by a user to change the position of the object being supported.